With even Microsoft struggling to make much impact on the smartphone world with Windows Phone, and BlackBerry's outlook looking less than brilliant, launching a new phone with an entirely new operating system might seem like a risky decision.

Jolla doesn't seem worried, though. The Finnish company reckons its Sailfish OS software -- which supports numerous Android apps -- together with its colorful, case-swapping phone, also called Jolla, will succeed where others haven't.

The Jolla phone is currently being shipped out to early preorder customers across Europe for 399 euros (around US$540), although Jolla couldn't say when it will be available anywhere else at the time of writing.

Design
With its two-tone split, the Jolla phone is distinctive. It looks almost like two phones squashed together. Both the glass front and plastic back are very plain, but I found the stark, minimalist design quite attractive -- particularly with the bright, lime green case.

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These back panels are interchangeable and have NFC chips, allowing different covers to automatically change themes and settings when they're clicked onto your phone. They link to your Jolla account to allow them to save your settings, which has the knock-on effect of stopping you from trading them with your friends. It's a neat idea, but I'm not sure it really adds anything over just manually selecting different themes.

The 4.5-inch display has a 960x540-pixel resolution. That's a little low, and it does result in small text under the icons looking a little fuzzy. Web pages didn't look as crisp as you'd see on other, higher-resolution phones. Given that the $179 Motorola Moto G packs in a higher 720p resolution, I'd like to see more pixels here.

The phone measures 131mm long, 68m wide, and is 9.9mm thick. It's hardly the slimmest phone around, nor is it the lightest, but it's easy enough to hold and more comfortable to type on one-handed than any of the 5- and 6-inch phablets.

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Volume and power buttons are on the side, with a 3.5mm headphone jack and Micro-USB port on the top. A microSD card is hidden under the back cover, allowing you to expand the 16GB of storage.

Sailfish OSThe phone runs Jolla's Sailfish OS, an offshoot of the MeeGo software that used to be found on old Nokia phones such as the N9. While the software has some visual similarities to MeeGo, it's functionally very different, and far removed from its Android or iOS rivals.

For one, there are no navigation buttons, so making your way around requires you to use various gestures. A double tap will wake the phone up and show you notifications. Swipe up and you'll see your recent apps, and keep swiping up to make your way to a grid of app icons. To return home from an app, swipe in from the left and it'll place the app in a multitasking panel. When going through menus or text message conversations, simply swiping back will return you to the previous page. A swipe up from below the screen shows a notifications panel.

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The multitasking panel can show up to nine app thumbnails for you to easily switch to, with four apps sitting below for quick access to crucial tools. Sailfish does not make use of big widgets across its home screen, so keen Android users might feel out of place here.

It's a fairly attractive interface, full of modern, minimalist text and rounded app icons, but there will be a sharp learning curve for those of you used to the simplicity of iOS. A quick user guide takes you through some of the key gestures when you first start the phone up, but you're still required to remember them all.

In my few hours with the phone, I felt I was able to get to grips with the basics, but performing simple tasks like connecting to Wi-Fi networks was awkward, and required an extra tap or swipe than it would performing the same task on Android. I also found that when closing apps to put them in the multitasking panel, they would sometimes reopen immediately afterward, as though they just didn't want to be closed. It's common for new software to have some bugs, but given that the phone is already on sale, I'd like to see it free of these little annoyances.

Android appsOne of the big issues with any new operating system is a lack of app support from developers. It's an issue that has plagued BlackBerry and continues to be a problem for Windows Phone -- Instagram has only just made its way to Windows Phone devices. Sailfish has a huge head start, however, as it's possible to run Android apps on the phone.

Although you can't access the Google Play store, as it's not accredited by Google, there are third-party app stores where you can find big Android titles such as Spotify, LinkedIn, Skype, Facebook, Twitter, Instagram, and many others. You can't get everything you'd find in the Play store on an Android phone -- Jolla couldn't tell me exactly how many Android apps are available for Sailfish -- but this shared functionality means there's already a better selection of apps on Sailfish than on BlackBerry.

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The apps themselves run exactly as they would do on a standard Android phone. Onscreen virtual navigation keys appear below the display to help you move around, although returning to home requires the same swipe in from the left.

An odd quirk is the phone's insistence on taking you back to the previously opened Android app before loading the one you've just clicked. While this is probably a necessary step as the apps are being "virtualized," rather than running natively, it does mean there's a delay before your app opens. If you're in a hurry, this could become annoying.

It's powered by a dual-core 1.4GHz processor which seemed powerful enough to offer a smooth interface. There's a 2,100mAh battery inside, which Jolla reckons will give up to 9 hours of 3G talk time; on the back you'll find an 8-megapixel camera. It has LTE connectivity for superfast data downloads, too.

OutlookThe Jolla phone is certainly an unusual piece of kit, with its two-tone design and Sailfish software. While an entirely new operating system for a phone might seem like a dangerous move for Jolla, its support for Android apps means it's already off to a decent start.